The present invention relates to combined plants consisting of a fluid production apparatus and a unit which consumes a fluid, in which at least one reaction occurs, and to the processes for operating such combined plants.
It is known from EP-A-0 758 733 to expand a product of a chemical reaction and to use the expansion energy to supercharge a stream of air intended for an air separation apparatus or a stream of nitrogen coming from the apparatus.
DE-A-3114842 describes a case in which the air intended for an air separation apparatus is compressed using the energy generated by a Rankine cycle.
U.S. Pat. No. 3,304,074 describes the expansion of the gas from the throat of a blast furnace in a turbine coupled to the main compressor of an air separation apparatus. The process makes no provision for the production of liquid.
French Patent Application FR 98/00724 in the name of the Applicant discloses a process in which an air supercharger is driven by a turbine in which a fluid available on the site (steam, waste gas from a furnace) is expanded.
EP-A-0 282 321 describes the generation of electricity by the expansion of a combustion product, some of the electricity feeding an air separation apparatus or a liquefier.
xe2x80x9cEngineering, Construction and Start-up of the ELCOGAS IGCC power plant at Puertollanoxe2x80x9d by Gasc et al., POWER-GEN EUROPE, June 1997 and many other articles disclose an integrated plant, comprising an air separation apparatus, a coal gasification unit and a gas turbine in which a gas from the unit is sent to a combustion unit and a gas-produced by the combustion is expanded in a gas turbine coupled to the common compressor of the air separation apparatus and the gas turbine. This system is used to generate energy which is exported, away from the integrated plant.
U.S. Pat. No. 3,950,957 describes an air separation apparatus integrated with a steam production apparatus. The steam turbine drives the air compressor, but this coupling is insufficient to meet all the energy requirements of the air separation apparatus. There is therefore no production of liquid directly from the separation unit.
DE-A-2930523 describes an air separation apparatus integrated with a steam production apparatus. One of the steam turbines drives the air compressor and the other a nitrogen compressor of the air separation apparatus. There is no production of liquid from the air separation apparatus and the compressed nitrogen is not sent to the steam production apparatus.
Certain reactions, such as the combustion of waste, make it possible to produce energy in an amount sometimes limited by expansion of waste gases or by expansion of steam heated by a boiler, where the waste gases burn, or by use in a gas motor.
In order to optimize the production of energy or to minimize the volume of waste gases for environmental purposes, oxygen is used in a large amount, and very often nitrogen for inerting requirements.
The energy consumed for separating the fluids from air and possibly compressing the gases output by the separation apparatus corresponding to the requirements of this process may be much less than the energy produced by the reaction or reactions and in balance this integrated plant may be an energy generator. Typically, 240 t/d of waste with 120 t/d of oxygen gives about 20 to 25 t/h of steam, which develops at most about 5 MW, some of this power being consumed by the air separation, provided that the excess steam available is not used for other purposes, for example for district heating in the periphery of this unit.
The object of the invention is to reduce the investment cost of an integrated plant while completely or partially eliminating the cost of connecting up the medium-voltage or high-voltage (MV or HV) motors and generators to the electric grid.
Another object of the invention is to improve the overall energy efficiency of the plant by eliminating the transformers, the MV or HV motors and the MV or HV generators of the prior art.
Another object of the invention is to allow more intelligent use of the energy produced by the plant when the electricity generated cannot be distributed or cannot be distributed under favourable economic conditions.
One subject of the invention is a combined plant comprising: at least one unit for consuming a fluid from the air, in which at least one reaction occurs, at least one apparatus for producing fluid from the air comprising an air separation apparatus having a main air compressor; means for sending at least one fluid from the air from the production apparatus to the unit and at least one first device with which at least one portion of a gas derived from the unit in which the reaction occurs is used to produce mechanical energy, the or one of the device(s) possibly driving the main air compressor,
characterized in that
i) a/the device drives at least the main air compressor and/or at least one compressor for compressing a gaseous product output by the air separation apparatus, the production apparatus comprises means for producing a component of air in liquid form, comprising means for withdrawing a liquid from the separation apparatus and at least the driven compressor and the device driving the compressor are connected, electrically, only to means of generating low-voltage electricity and/or means of consuming low-voltage electricity and are connected to means of generating and consuming medium-voltage and high-voltage electricity only through means of generating low-voltage electricity and/or means of consuming low-voltage electricity, and/or
ii) a/the device drives at least one cycle compressor of means of liquefaction of a gas coming from the air separation apparatus and/or
iii) a/the device drives at least one compressor for compressing a gas output by or intended for the unit.
Thus, the device is not connected directly to a means of generating medium-voltage or high-voltage electricity or to a means of consuming medium-voltage or high-voltage electricity.
However, the low-voltage electricity, needed for coolant pumps and other accessories, will come from a source of medium-voltage or high-voltage electricity by means of a transformer.
The low voltage is voltage below 1000 V, the medium voltage is between 1000 V and 15 kV and the high voltage is above 15 kV.
Preferably, the air separation apparatus and/or the unit and/or the liquefaction means are not connected directly to means of generating or consuming medium-voltage or high-voltage electricity, once in operation. They may be permanently connected to a means of generating or consuming low-voltage electricity. During the start-up of the air separation apparatus or of the unit or of the liquefaction means, these could be connected to means of generating and/or consuming medium-voltage or high-voltage electricity.
Since the energy production of the unit for the device(s) may exceed the requirements of the apparatus for production of fluid from the air, in order to produce gases intended for the unit and/or for the unit itself this energy may be utilized by producing additional liquid directly from the air separation apparatus or from the liquefaction means.
The gaseous product output by the separation apparatus may be air or a gas enriched with nitrogen, with oxygen or with argon.
The device may drive, at the same time as the main air compressor, an air supercharger possibly integrated with this compressor (i.e. on the same shaft as the compressor).
In a second device, a portion of a gas derived from the unit is used to produce mechanical energy for driving at least one second compressor.
The second compressor may compress air intended for an air separation apparatus or a gas coming from an air separation apparatus or a cycle gas for the liquefaction of a gas coming from the separation apparatus.
In the case of ii) and iii), the production apparatus may comprise means for producing a liquid product, these means possibly consisting of means of liquefaction of a gas coming from the separation apparatus or means for withdrawing liquid from the separation apparatus; the device driving the compressor and the driven compressor are therefore not connected directly to a means of generating medium-voltage or high-voltage electricity and are not connected directly to a means of consuming medium-voltage or high-voltage electricity. On the other hand, they are connected to medium-voltage and/or high-voltage means of generation and of consumption through the low-voltage means of generation and/or of consumption.
The first or second device is a turbine, a gas turbine or a gas motor.
The plant may comprise at least:
a) means for sending compressed air from a compressor of the separation apparatus to the unit and/or
b) means for sending a stream of gaseous oxygen from the separation apparatus to the unit and/or
c) means for sending liquid oxygen from the separation apparatus to the unit and/or
d) means for sending liquid nitrogen from the liquefaction means or from the separation apparatus to the unit and/or
e) means for sending gaseous nitrogen from the separation apparatus to the unit and/or
f) means for sending gaseous or liquid argon from the separation apparatus to the unit.
All the energy not consumed by the unit or by other apparatuses associated with the unit (such as the air separation apparatus) and generated by the device(s), may serve for driving one or more compressors of the air distillation apparatus.
All the energy for compressing the gases from the air distillation apparatus (feed air or gaseous or cycle products) may be delivered by the device(s) of the plant.
The main compressor may be a dedicated compressor feeding only the air separation apparatus or may feed at least one apparatus other than the air separation apparatus.
Optionally, the air separation apparatus produces at least one gas or at least one liquid not intended for the unit and/or for the liquefaction means.
The fluid from the air may or may not participate in the reaction which is carried out in the unit.
The liquefaction means are means for liquefying a gas coming from the air separation apparatus. They comprise a liquefaction cycle with at least one refrigeration turbine which expands the pressurized gas to be liquefied or another source of refrigeration, such as a stream of LNG to be vaporized.
Another aspect of the invention provides an integrated process for production of fluid from the air and of at least one reaction, in which process a fluid from the air, generated by an apparatus for production of fluid from the air comprising an air separation apparatus having a main air compressor, is sent to a unit, which consumes a fluid from the air, in which a reaction is carried out, at least one gas derived from the reaction produces mechanical energy by means of a device and the device drives at least one compressor, possibly the main air compressor of the air separation apparatus,
characterized in that,
i) a/the device drives at least the main air compressor of the air separation apparatus and/or at least one compressor for compressing a gaseous product output by the air separation apparatus, the apparatus for production of fluid from the air produces at least one component of air in liquid form by withdrawing a liquid from the air separation apparatus and at least the device and the compressor consume and/or generate only low-voltage electricity, this low-voltage electricity coming from or being intended for a source of medium-voltage or high-voltage electricity and/or
ii) a/the device drives at least a cycle compressor for liquefying a gas coming from the air separation apparatus and/or
iii) a/the device drives at least a gas compressor output by or intended for the unit.
The gaseous product output by the separation apparatus may be nitrogen or a gas enriched with nitrogen, with oxygen or with argon.
Preferably
a) compressed air is sent from a compressor of the separation apparatus to the unit and/or
b) a stream of possibly compressed gaseous oxygen is sent from the separation apparatus to the unit and/or
c) a stream of possibly pressurized liquid oxygen is sent from the separation apparatus to the unit and/or
d) possibly pressurized liquid nitrogen is sent from the liquefaction means and/or from the separation apparatus to the unit and/or
e) possibly compressed gaseous nitrogen is sent from the separation apparatus to the unit and/or
f) possibly pressurized gaseous or liquid argon is sent from the separation apparatus to the unit.
The apparatus for production of gas from the air comprises an air separation apparatus and optionally means of liquefaction of a gas coming from the separation apparatus.
The separation apparatus may consist of a main air compressor, a heat exchanger, at least one turbine for expanding fluid from the air and at least one double air distillation column.
A second device which produces mechanical energy may drive a second compressor.
The second compressor may compress air intended for an air separation apparatus or a gas coming from an air separation apparatus or a cycle gas for liquefaction of a gas coming from the separation apparatus or a gas output by or intended for the unit.
The main compressor may be a dedicated compressor feeding only the air separation apparatus or may feed at least one apparatus other than the air separation apparatus.
Optionally, the air separation apparatus produces at least one gas not intended for the unit and for the means of liquefaction of a gas.
It will be understood that a device which produces mechanical energy may drive one or more compressors of the plant.
The unit and/or the separation apparatus and/or the liquefaction means may consume and/or generate only low-voltage electricity. This low-voltage electricity will come from or be sent to a source of medium-voltage or high-voltage electricity.
In this way, an apparatus for production of fluid from the air may operate without a direct supply of medium-voltage or high-voltage electrical energy from the outside; this allows the costs to be appreciably reduced. The same may apply to the unit which consumes a fluid from the air or the liquefaction means. Of course, there will be an indirect supply of medium-voltage or high-voltage electrical energy to the transformers delivering the low-voltage electricity to the apparatus or to certain elements of the apparatus.
A fluid from the air is either gaseous or liquid air or is a gas or a liquid derived from air by redistillation or another means of separation.